Electrostatic images formed on an electrophotographic photoconductor and an electrostatic recording medium are generally developed by a wet-type development method using a liquid developer or a dry-type development method by using (i) a mono-component type dry developer consisting of a toner comprising a coloring agent such as a dye or pigment and a binder resin in which the coloring agent is dispersed, or with addition of a charge controlling agent thereto when necessary, or (ii) a two-component type dry developer comprising the above-mentioned toner and solid carrier particles. These development methods have their own advantages and disadvantages, but the dry-type development method is more widely employed.
Conventionally, such toners are prepared by kneading a resin component and a coloring agent component at or above a temperature at which these two components are fused, cooling the kneaded mixture, crushing the same by a mechanical or air-impaction crusher, and classifying the crushed particles. However, this method is complicated in the manufacturing steps and the yield of the toner produced is low.
In another conventional method of producing such toners, a coloring agent, a dispersion-stabilizing agent, and a surface active agent are dispersed in an organic solvent solution of a polymerizable monomer, and the polymerizable monomer is subjected to suspension polymerization as proposed in Japanese Patent Publications No. 51-14895 and No. 47-51830. This method has the advantage over other methods that toner particles can be prepared by a single process. However, agents employed, such as dispersion-stabilizing agent and surface active agent, which cause the charging characteristics and preservability of the toner particles to deteriorate, remain on the surface of the toner particles, and those agents are extremely difficult to remove from the toner particles.
In a further conventional method of producing the toner particles, resin particles are immersed in a dye solution and dyed by the solution as proposed in Japanese Laid-Open Patent Applications No. 50-46333, No. 1-103631, No. 56-154738, No. 63-106667 and No. 64-90454. An advantage of this method over other conventional methods is that the number of the production steps is small. However this method has not yet been studied to the extent that it can be confirmed that the method can be used sufficiently in practice.